fix: properly initialize rx.Field annotated backend vars in mixin states (#5909)

* fix: properly initialize rx.Field annotated backend vars in mixin states

* fix: check mixin_cls instead of cls

* add some basic tests

* i missed this one

Author: benedikt-bartscher

reflex/state.py

@@ -523,15 +523,17 @@ def __init_subclass__(cls, mixin: bool = False, **kwargs):
 
         new_backend_vars = {
             name: value if not isinstance(value, Field) else value.default_value()
-            for name, value in list(cls.__dict__.items())
-            if types.is_backend_base_variable(name, cls)
+            for mixin_cls in [*cls._mixins(), cls]
+            for name, value in list(mixin_cls.__dict__.items())
+            if types.is_backend_base_variable(name, mixin_cls)
         }
         # Add annotated backend vars that may not have a default value.
         new_backend_vars.update({
             name: cls._get_var_default(name, annotation_value)
-            for name, annotation_value in cls._get_type_hints().items()
+            for mixin_cls in [*cls._mixins(), cls]
+            for name, annotation_value in mixin_cls._get_type_hints().items()
             if name not in new_backend_vars
-            and types.is_backend_base_variable(name, cls)
+            and types.is_backend_base_variable(name, mixin_cls)
         })
 
         cls.backend_vars = {
@@ -579,9 +581,6 @@ def __init_subclass__(cls, mixin: bool = False, **kwargs):
                     cls.computed_vars[name] = newcv
                     cls.vars[name] = newcv
                     continue
-                if types.is_backend_base_variable(name, mixin_cls):
-                    cls.backend_vars[name] = copy.deepcopy(value)
-                    continue
                 if events.get(name) is not None:
                     continue
                 if not cls._item_is_event_handler(name, value):

tests/units/test_state.py

@@ -110,7 +110,14 @@ class Object(Base):
     prop2: str = "hello"
 
 
-class TestState(BaseState):
+class TestMixin(BaseState, mixin=True):
+    """A test mixin."""
+
+    mixin: rx.Field[str] = rx.field("mixin_value")
+    _mixin_backend: rx.Field[int] = rx.field(default_factory=lambda: 10)
+
+
+class TestState(TestMixin, BaseState):  # pyright: ignore[reportUnsafeMultipleInheritance]
     """A test state."""
 
     # Set this class as not test one
@@ -342,6 +349,7 @@ def test_class_vars(test_state):
         "fig",
         "dt",
         "asynctest",
+        "mixin",
     }
 
 
@@ -367,7 +375,7 @@ def test_event_handlers(test_state):
     assert all(key in cls.event_handlers for key in expected_keys)
 
 
-def test_default_value(test_state):
+def test_default_value(test_state: TestState):
     """Test that the default value of a var is correct.
 
     Args:
@@ -378,6 +386,10 @@ def test_default_value(test_state):
     assert test_state.key == ""
     assert test_state.sum == 3.15
     assert test_state.upper == ""
+    assert test_state._backend == 0
+    assert test_state.mixin == "mixin_value"
+    assert test_state._mixin_backend == 10
+    assert test_state.array == [1, 2, 3.15]
 
 
 def test_computed_vars(test_state):
@@ -735,7 +747,7 @@ def test_set_dirty_substate(
     assert grandchild_state.dirty_vars == set()
 
 
-def test_reset(test_state, child_state):
+def test_reset(test_state: TestState, child_state: ChildState):
     """Test resetting the state.
 
     Args:
@@ -771,6 +783,8 @@ def test_reset(test_state, child_state):
         "mapping",
         "dt",
         "_backend",
+        "mixin",
+        "_mixin_backend",
         "asynctest",
     }
 

tests/units/utils/test_format.py

@@ -602,6 +602,7 @@ def test_format_query_params(input, output):
                     "key" + FIELD_MARKER: "",
                     "map_key" + FIELD_MARKER: "a",
                     "mapping" + FIELD_MARKER: {"a": [1, 2, 3], "b": [4, 5, 6]},
+                    "mixin" + FIELD_MARKER: "mixin_value",
                     "num1" + FIELD_MARKER: 0,
                     "num2" + FIELD_MARKER: 3.15,
                     "obj" + FIELD_MARKER: {"prop1": 42, "prop2": "hello"},